Fly-ash is a byproduct of coal combustion that poses significant environmental hazards when improperly disposed of. The combination of fly-ash and lime is generally utilized for stabilization of pavement subgrade, but limited research is available for improvement of foundation soil. This study aims primarily to find out the optimum amount of clay + fly-ash + lime required to improve the properties of clayey soil. Samples were prepared with five different percentages of lime such as 1%, 2%, 3%, 4% and 5% added, respectively, with different percentages of fly-ash such as 24%, 23%, 22%, 21%, and 20% keeping clayey soil constant at 75%. Unconfined compressive strength (UCS) test was performed on cured samples after 8 days, 14 days, and 28 days from which optimum combination of stabilized layer was found to be 75% clay + 23% fly-ash + 2% lime and 38% water content. The main purpose of the study was to determine the optimal thickness of stabilized layer required to be placed over the clayey soil. To achieve the objective, 0.6 m thick soft clayey soil bed was prepared in a modal test tank of size 1 m × 1 m × 1 m. Then the clay + fly-ash + lime stabilized layer compacted at optimum proportion was placed over the clayey soil bed at different H/B ratio such as 0, 0.25, 0.5, 0.75, and 1, where H represents the thickness of stabilized layer and B denotes the width of footing. Vertical load test was performed on 0.2 m × 0.2 m shallow foundation, and load-settlement graphs were plotted. The ultimate load was observed, respectively, to be 1.48 kN, 2.68 kN, 3 kN, 4 kN, 12 kN. Numerical analysis was also performed using PLAXIS-3D software to verify the results. It is observed from the results that if a stabilized layer of thickness equals to the width of shallow foundation which is placed over the clayey soil, the ultimate load-carrying capacity increases to 8.11 times compared to unstabilized clayey soil.